My dog does not seem to have a flea problem (I see one every once in a while) but he has had tapeworms 5 times, 3 of which were in the last 3 months. I am forever checking him for fleas and immediately look if he scratches or bites at his skin to keep him from swallowing one that may be there. I am frustrated because I don't know why he is continuing to get tapeworms and I hate to keep exposing him to the medicine for their treatment. I don't know if it will have long-term negative effects if used this many times.